NFS: Don't run wake_up_bit() when nobody is waiting...
"perf lock" shows fairly heavy contention for the bit waitqueue locks when doing an I/O heavy workload. Use a bit to tell whether or not there has been contention for a lock so that we can optimise away the bit waitqueue options in those cases. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
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@ -155,9 +155,12 @@ nfs_page_group_lock(struct nfs_page *req, bool nonblock)
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if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
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return 0;
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if (!nonblock)
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if (!nonblock) {
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set_bit(PG_CONTENDED1, &head->wb_flags);
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smp_mb__after_atomic();
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return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
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TASK_UNINTERRUPTIBLE);
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}
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return -EAGAIN;
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}
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@ -175,6 +178,10 @@ nfs_page_group_lock_wait(struct nfs_page *req)
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WARN_ON_ONCE(head != head->wb_head);
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if (!test_bit(PG_HEADLOCK, &head->wb_flags))
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return;
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set_bit(PG_CONTENDED1, &head->wb_flags);
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smp_mb__after_atomic();
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wait_on_bit(&head->wb_flags, PG_HEADLOCK,
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TASK_UNINTERRUPTIBLE);
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}
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@ -193,6 +200,8 @@ nfs_page_group_unlock(struct nfs_page *req)
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smp_mb__before_atomic();
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clear_bit(PG_HEADLOCK, &head->wb_flags);
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smp_mb__after_atomic();
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if (!test_bit(PG_CONTENDED1, &head->wb_flags))
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return;
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wake_up_bit(&head->wb_flags, PG_HEADLOCK);
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}
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@ -383,6 +392,8 @@ void nfs_unlock_request(struct nfs_page *req)
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smp_mb__before_atomic();
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clear_bit(PG_BUSY, &req->wb_flags);
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smp_mb__after_atomic();
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if (!test_bit(PG_CONTENDED2, &req->wb_flags))
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return;
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wake_up_bit(&req->wb_flags, PG_BUSY);
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}
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@ -465,6 +476,10 @@ void nfs_release_request(struct nfs_page *req)
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int
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nfs_wait_on_request(struct nfs_page *req)
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{
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if (!test_bit(PG_BUSY, &req->wb_flags))
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return 0;
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set_bit(PG_CONTENDED2, &req->wb_flags);
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smp_mb__after_atomic();
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return wait_on_bit_io(&req->wb_flags, PG_BUSY,
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TASK_UNINTERRUPTIBLE);
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}
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@ -33,6 +33,8 @@ enum {
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PG_UPTODATE, /* page group sync bit in read path */
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PG_WB_END, /* page group sync bit in write path */
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PG_REMOVE, /* page group sync bit in write path */
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PG_CONTENDED1, /* Is someone waiting for a lock? */
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PG_CONTENDED2, /* Is someone waiting for a lock? */
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};
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struct nfs_inode;
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